In the manufacture of semiconductor chips, there are various steps in the process. One step relates to circuitizing or etching of the semiconductor material to implement the integrated circuit design. While the prior known techniques employed to accomplish such a step in the process may have been satisfactory for some applications, there have been attempts proposed for improving the circuitizing step in the manufacturing process.
One proposed attempt has been to utilize X-ray radiation to achieve the circuitizing step. Such an approach has proven to be costly, and is currently undergoing further research and development work in an attempt to achieve the desired results.
In general, conventional semiconductor etching techniques generally include exposing a photoresist-coated substrate to an impinging light beam. However, with the ever increasing miniaturization of the semiconductor integrated circuitry, the size of circuit details are becoming so small that they are of a similar order of magnitude as the size of the wavelength of the impinging light beam itself. Thus, the impinging light becomes diffracted, and irregularities in the resulting product can occur.
Furthermore, due to the relatively low intensity of nonlaser sources of impinging light, the required exposure time is extended so as to convey the necessary energy for use in the etching process. Thus, the etching process is not only delayed, but the risk of impurities infiltration is increased substantially.
Therefore, there is a need for an incoherent light source and a method of using it, which further render the semiconductor etching processes compatible with modern techniques. In this regard, undesirable diffraction caused by impinging coherent light beams would be greatly reduced, if not minimized.
Thus, at the present time, there has not been any approach which has proven to be an improvement in circuitizing semiconductors, in a more effective and efficient manner. Clearly, there has not been even a suggestion of a cost effective approach, which should constitute an improvement in present day technology, employing mass production techniques.
In another stage in the manufacturing process of semiconductors, such as semiconductor chips, semiconductor materials, in the form of thin wafers, must be annealed In such a step in the overall process, the resulting annealed wafer has not been annealed in an entirely satisfactory manner. In this regard, in prior known annealing steps, it has been recognized the importance of uniformity in the activation in the wafer to be annealed, of the semiconductor implanted dopants, such as boron, over an entire semiconductor wafer surface
In the past, such dopant activation has been achieved by a steady-state furnace annealing method, wherein a semiconductor wafer implanted with a dopant is placed in an annealing oven. The temperature of the oven is then slowly raised in a controlled manner for a long period of time, such as one half of an hour. After maintaining the temperature at a desired elevated temperature, the temperature of the oven is then decreased slowly and controllably for another long period of time, such as another one half hour period. Thereafter, the annealed semiconductor wafers are removed from the oven.
While the steady-state furnace annealing method may be satisfactory for some applications, it has not proven entirely acceptable in the manufacturing of certain semiconductor circuits and devices. In this regard, state of the art semiconductor devices and circuits have become increasingly smaller in size, such as about 1 .mu.m. As these dimensions diminished in size, the need to form shallower semiconductor junctions with minimal dopant diffusion, has increased. It has been found, however, that dopants, such as boron, tend to diffuse rapidly during the high temperature annealing process used in the steady-stat furnace method. Thus, the consequent redistribution of the dopant has exceeded the limits of acceptability for at least some MOS-VLSI devices, and especially high speed devices which require higher dopant doses.
In order to reduce or minimize the amount of redistribution of the dopant, several different techniques have been attempted. One such attempted technique includes using a halogen arc lamp to heat and anneal the semiconductor wafer rapidly. While such an approach employing a halogen lamp has shown that full activation of moderate dose implants of boron, could be achieved at temperatures of 1000.degree. C. in about ten seconds, it has proven to be less than totally satisfactory, particularly where higher dose dopants have been required. In this regard, it was found that uniformity of activation was unacceptable in higher doses, until the annealing time was increased to at least 60 seconds. However, by increasing the annealing time, the consequent dopant redistribution approaches 0.1 .mu.m, which redistribution is near the limit of acceptability for MOS-VLSI device, but too large for the very high speed bipolar devices.
Therefore, it would be highly desirable to have a technique for overcoming the excessively diffusive redistribution problem associated with high dosage dopant implanted semiconductor devices. Such a technique or method should achieve uniformity of activation of implanted dopants over large wafers with minimal, or at least greatly reduced, diffusive redistribution.
Another attempted solution which has also proven to be less than satisfactory, is the use of an isothermal annealer. In this method, infrared radiation from a resistance heat sheet of graphite is used to heat the wafer to be annealed. This technique resulted in production of semiconductor devices comparable to those obtained by employing furnace annealing equipment, but has not proven at all satisfactory for the smaller high dopant semiconductor devices.
Yet another attempted solution to the concerns associated with the prior art, included the use of a laser to scan and to heat the semiconductor wafer rapidly. This method has also proven to be less than satisfactory, since it was discovered that in order to achieve uniform activation of the dopant over the entire semiconductor material surface, the laser scan lines were required to be overlapped. It was also found, however, that if the scan lines are heavily overlapped, microfractures are produced which act as strong sources for dislocation generation, thereby rendering the device defective. In this regard, undesirable non-uniform annealing of the semiconductor substrates occurs, since certain areas of the substrates receive a relatively excessive flux of energy. Moreover, the cost of such lasers required to achieve the necessary rapid heating, has proven to be a relatively expensive and complex process, and otherwise less than satisfactory. In this regard, trained and skilled personnel are required to operate the expensive laser equipment.
In general, the use of a coherent light beam, such as a conventional laser beam, is subject to diffraction, which further reduces the performance of the annealing process because of the nonuniformities in the diffraction pattern. Additionally, an overly extended exposure to the laser beam can cause micro-cracks or micro-crystalline damage to the substrate. Thus, the prior known laser annealing processes do not produce entirely satisfactory results for some applications. In this regard, the resulting products are oftentimes defective, and an undesirably high reject rate does occur all too frequently. Thus, known processes frequently produce unwanted side affects, are relatively time consuming, and are costly due to the large number of rejects.
Therefore, there is a need for an annealing process and equipment which prevent, or at least greatly eliminate the unwanted side affects. Such a new annealing technique should be relatively efficient and expedient.
As one type of laser proposed for annealing semiconductors, is the excimer laser. However, such a prior known excimer laser system, as hereinafter described in greater detail, has only been proposed, and has not been employed to any great extent in the actual production of semiconductors. In this regard, such systems have not been entirely practical, because of their inherent low efficiency, and low throughput. Thus, the cost to operate such a system is prohibitively high. Additionally, the cost of manufacturing such a system is also prohibitively high, and therefore uneconomical to both construct and to use in modern mass production technology. Also, the previously mentioned problems associated with laser annealing techniques apply to the excimer laser annealing techniques. For example, the problem of diffraction is equally applicable to an excimer laser technique.
Therefore, it would be highly desirable to have a method for achieving the uniform activation of implanted dopants in a rapid manner, without damaging the semiconductor wafer being annealed. Such a technique should be able to be implemented at a relative low cost.